A. Field of Invention
This invention relates to apparatuses and methods for treating glaucoma.
B. Description of the Related Art
It is known in the art that the treatment of glaucoma consists in lowering the intraocular pressure to a level that is tolerable for the optic nerve so that the progression of damage and visual loss is halted.
Glaucoma is a significant public health problem, because glaucoma is a major cause of blindness. The blindness that results from glaucoma involves both central and peripheral vision and has a major impact on an individual""s ability to lead an independent life.
Glaucoma is an optic neuropathy (a disorder of the optic nerve) that usually occurs in the setting of an elevated intraocular pressure. The pressure within the eye increases and this is associated with changes in the appearance (xe2x80x9ccuppingxe2x80x9d) and function (xe2x80x9cblind spotsxe2x80x9d in the visual field) of the optic nerve. If the pressure remains high enough for a long enough period of time, total vision loss occurs. High pressure develops in an eye because of an internal fluid imbalance.
The eye is a hollow structure that contains a clear fluid called xe2x80x9caqueous humor.xe2x80x9d Aqueous humor is formed in the posterior chamber of the eye by the ciliary body at a rate of approximately 2.5 microliters per minute. The fluid, which is made at a fairly constant rate, then passes around the lens, through the pupillary opening in the iris and into the anterior chamber of the eye. Once in the anterior chamber, the fluid drains out of the eye through two different routes. In the xe2x80x9cuveoscleralxe2x80x9d route, the fluid percolates between the muscle fibers of the ciliary body. This route accounts for approximately ten percent of the aqueous outflow in humans. The primary pathway for aqueous outflow in humans in through the xe2x80x9ccanalicularxe2x80x9d route that involves the trabecular meshwork and Schlemm""s canal.
The trabecular meshwork and Schlemm""s canal are located at the junction between the iris and the sclera. This junction or corner is called xe2x80x9cthe angle.xe2x80x9d The trabecular meshwork is a ring of tissue, which is wedge-shaped in cross-section, that runs around the circumference of the eye. It is composed of collagen beams arranged in a three-dimensional sieve-like structure. The beams are lined with a monolayer of cells called trabecular cells. The spaces between the collagen beams are filled with an extracellular substance that is produced by the trabecular cells. These cells also produce enzymes that degrade the extracellular material. Schlemm""s canal is adjacent to the trabecular meshwork. The outer wall of the trabecular meshwork coincides with the inner wall of Schlemm""s canal. Schlemm""s canal is a tube-like structure that runs around the circumference of the cornea.
The aqueous fluid travels through the spaces between the trabecular beams, across the inner wall of Schlemm""s canal into the canal, through a series of about twenty-five collecting channels that drain from Schlemm""s canal and into the episcleral venous system. In a normal situation, aqueous production is equal to aqueous outflow and intraocular pressure remains fairly constant in the 15 to 21 mmHg range. In most cases of glaucoma, the resistance through the canalicular outflow system is abnormally high.
In primary open angle glaucoma, which is the most common form of glaucoma, the abnormal resistance is believed to be along the outer aspect of the trabecular meshwork and the inner wall of Schlemm""s canal. It is believed that an abnormal metabolism of the trabecular cells leads to an excessive buildup of extracellular materials or a buildup of abnormally xe2x80x9cstiffxe2x80x9d materials in this area. Histopathology of glaucoma eyes also demonstrates a collapse of Schlemm""s canal. Primary open angle glaucoma accounts for approximately eighty-five percent of all glaucoma. Other forms of glaucoma (such as angle closure glaucoma and secondary glaucoma) also involve decreased outflow through the canalicular pathway, but the increased resistance is from other causes such as mechanical blockage, inflammatory debris, cellular blockage, etc.
With the increased resistance, the aqueous fluid builds up because it cannot exit fast enough. As the fluid builds up, the intraocular pressure (IOP) within the eye increases. The increased IOP compresses the axons in the optic nerve and also may compromise the vascular supply to the optic nerve. The optic nerve carries vision from the eye to the brain. Some optic nerves seem more susceptible to IOP than others. While research is investigating ways to protect the nerve from an elevated pressure, the only therapeutic approach currently available in glaucoma is to reduce the intraocular pressure.
The clinical treatment of glaucoma is approached in a step-wise fashion. Medication often is the first treatment option. Administered either topically or orally, these medications work to either reduce aqueous production or to increase outflow. Currently available medications have many serious side effects including: congestive heart failure, respiratory distress, hypertension, depression, renal stones, aplastic anemia, sexual dysfunction, and death. Compliance with medication is a major problem, with estimates that over half of glaucoma patients do not follow their correct dosing schedules.
When medication fails to adequately reduce the pressure, laser trabeculoplasty often is performed. In laser trabeculoplasty, thermal energy from a laser is applied to a number of noncontiguous spots in the trabecular meshwork. It is believed that the laser energy stimulates the metabolism of the trabecular cells in some way, and changes the extracellular material in the trabecular meshwork. In approximately eighty percent of patients, aqueous outflow is enhanced and IOP decreases. However, the effect often is not long lasting and fifty percent of patients develop an elevated pressure within five years. The laser surgery is not usually repeatable with beneficial effect on pressure. In addition, laser trabeculoplasty is not an effective treatment for young primary open angle glaucoma patients, nor is it effective for angle closure glaucoma and many secondary glaucomas.
If laser trabeculoplasty does not reduce the pressure enough, then filtering surgery is generally performed. With filtering surgery, a hole is made in the sclera in the angle region. This hole allows the aqueous fluid to leave the eye through an alternate route.
The most commonly performed filtering procedure is a trabeculectomy. In a trabeculectomy, a posterior incision is made in the conjunctiva, the transparent tissue that covers the sclera. The conjunctiva is rolled forward, exposing the sclera at the limbus. A partial thickness scleral flap is made and dissected approximately one-half thickness into the cornea. The anterior chamber is entered beneath the scleral flap and a section of deep sclera and trabecular meshwork is excised. An iridectomy, a hole in the thus exposed iris, is made. The scleral flap is loosely sewn back into place. The conjunctival incision is tightly closed. Post-operatively, the aqueous fluid passes through the hole, beneath the scleral flap, and collects in an elevated space beneath the conjunctiva called a filtration bleb. The fluid then is either absorbed through blood vessels in the conjunctiva or traverses across the conjunctiva into the tear film.
Trabeculectomy is associated with many problems. Fibroblasts that are present in the episclera proliferate and migrate, and can scar down the scleral flap. Failure from scarring may occur, particularly in children, blacks, and young adults. Of eyes that have an initially successful trabeculectomy, many will fail from scarring within three to five years after surgery. To minimize fibrosis, surgeons now are applying antifibrotic agents such as mitomycin C (MMC) and 5-fluorouracil (5-FU) to the scleral flap at the time of surgery. The use of these agents has increased the success rate of trabeculectomy, but also has increased the prevalence of hypotony, and other serious complications. Hypotony is a problem that develops when aqueous flows out of the eye too fast, the eye pressure drops too low (usually less than 6.0 mmHg), and the structure of the eye collapses and vision decreases.
Trabeculectomy creates a pathway for aqueous fluid to escape to the surface of the eye and into the blood stream. At the same time, it creates a pathway for bacteria that normally live on the surface of the eye and eyelids to get into the eye. If this happens, an internal eye infection, called endophthalmitis, can occur. Endophthalmitis can occur anytime after trabeculectomy. The risk increases with the thin blebs that develop after the use of MMC and 5-FU. Another factor that contributes to infection is the placement of a bleb. Eyes that have trabeculectomy performed at the lower limbus have about five times the risk of eye infection than eyes that have a bleb superiorly protected by the upper lid. Therefore, trabeculectomy is usually performed superiorly under the eyelid, in either the nasal or temporal quadrant.
In addition to scarring, hypotony, and infection, there are other complications of trabeculectomy. The bleb can tear and lead to profound hypotony. The bleb can be irritating and can disrupt the normal tear film, leading to blurred vision and discomfort. Patients with blebs generally cannot wear contact lenses. The overwhelming majority of the complications from trabeculectomy stem from the fact that fluid is being diverted from inside the eye to the external surface of the eye, resulting in a bleb.
When trabeculectomy does not successfully lower the eye pressure, the next surgical step often is an aqueous shunt device. An aqueous diversion device of the prior art is a silicone tube that is attached at one end to a plastic (polypropylene or other synthetic material) plate. With an aqueous shunt device, an incision is made in the conjunctiva and Tenons, exposing the sclera. The plastic plate is sewn to the surface of the eye posteriorly, usually over the equator between two rectus muscles. A full thickness hole is made into the eye at the limbus, usually with a needle of approximately 22 gauge. The tube, which is connected to the plate, is inserted into the eye through this hole. The external portion of the tube is covered with either donor sclera or preserved pericardium. The conjunctival and Tenons incisions are closed tightly. Many problems exist with the current technology of aqueous shunt devices including scarring, failure, hypotony, corneal decompensation, tube erosion, suprachoroidal effusion and/or hemorrhage, and infection.
With prior art aqueous diversion devices, aqueous drains out of the eye through the silicone tube to the surface of the eye at the location of the plate or reservoir. Deeper orbital tissues then absorb the fluid. The outside end of the tube is protected from fibroblasts and scarring by the plastic plate. Many complications are associated with aqueous shunt devices. A thickened wall of scar tissue that develops around the plastic plate offers some resistance to outflow and in many eyes limits the reduction in eye pressure. In some eyes, hypotony develops because the flow through the tube is not restricted. Many physicians tie an absorbable suture around the tube and wait for the suture to dissolve post-operatively, at which time enough scar tissue has hopefully formed around the plate. Some devices contain a pressure-sensitive valve within the tube, although these valves may not function properly. The surgery involves operating in the posterior orbit and many patients develop an eye muscle imbalance and double vision. With prior art aqueous shunt devices, a pathway is created for bacteria to get into the eye and endophthalmitis can occur.
The prior art includes a number of such aqueous shunt devices, such as U.S. Pat. No. 4,936,825 (implanting in the cornea and limbal area a device partially embedded and partially extending anteriorly), U.S. Pat. No. 5,127,901 (directed to a transscleral shunt from the anterior chamber to the subconjunctival space), U.S. Pat. No. 5,180,362 (teaching a helical steel implant that is placed to provide drainage from the anterior chamber to the subconjunctival space), and U.S. Pat. No. 5,433,701 (apparatus includes an anterior portion configured for implantation through a scleral tunnel such that a leading edge thereof is within the anterior chamber).
In addition to the prior art aqueous shunt devices described above, other prior art devices for glaucoma surgery have used setons, or other porous, wick-like components to divert and convey excess aqueous from the anterior chamber to the exterior ocular surface. Examples include U.S. Pat. Nos. 4,634,418 and 4,787,885(teaching the surgical treatment of glaucoma using an implant that consists of a triangular seton (wick)), and U.S. Pat. No. 4,946,436, (teaching the use of a porous device to shunt anterior chamber to subscleral space). These patents do not teach placement in Schlemm""s canal.
Some prior art references for glaucoma management have been directed at Schlemm""s canal, but these have not involved the placement of long-term, indwelling shunts. U.S. Pat. No. 5,360,399 (teaches the temporary placement of a plastic or steel tube with preformed curvature in Schlemm""s canal with injection of a viscous material through the tube to hydraulically expand and hydrodissect the trabecular meshwork). The tube is removed from the canal following injection. Because the tube is directed outwardly from the eye for injection access, the intersection of the outflow element with the preformed curved element within Schlemm""s canal is at about a 90 degree angle relative to the plane of the curvature, and 180 degrees away from the anterior chamber. Therefore, at no time does any portion of the ""399 device communicate with the anterior chamber. Furthermore, relative to that portion within Schlemm""s canal, this tube has a larger diameter injection cuff element, which serves as an adapter for irrigation. Therefore, this device is not adapted for shunting aqueous between the anterior chamber and Schlemm""s canal.
Most of the problems that have developed with current glaucoma treatment devices and procedures have occurred because aqueous fluid is drained from inside of the eye to the surface of the eye. A need exists, then, for a more physiologic system to enhance the drainage of aqueous fluid from the anterior chamber into Schlemm""s canal. In the vast majority of glaucoma patients, the resistance problem lies between Schlemm""s canal and the anterior chamber. The canal itself, the collecting channels, and the episcleral venous system all are intact. Enhancing aqueous flow directly into Schlemm""s canal would minimize the scarring that usually occurs with external filtration procedure since the internal angle region is populated with a single line of nonproliferating trabecular cells. Enhancing aqueous flow directly into Schlemm""s canal would minimize hypotony since the canal is part of the normal outflow system and is biologically engineered to handle the normal volume of aqueous humor. Enhancing aqueous flow directly into Schlemm""s canal would eliminate complications such as endophthalmitis and leaks.
The present invention is a method and apparatus for treating glaucoma. The present invention treats glaucoma by lowering intraocular pressure in the eye so that the pressure level is tolerable for the optic nerve, which in turn, slows or stops the progression of damage and visual loss.
According to one aspect of the invention, a seton conducts aqueous directly from the anterior chamber to Schlemm""s canal so that it can drain directly into the aqueous veins leading to the venous circulation. A seton for lowering intraocular pressure of an associated eye comprises a first tube adapted to be inserted into an associated anterior chamber of the eye; and, two wing tubes extending from the first tube. The two wing tubes are adapted to be inserted into Schlemm""s canal. The two wing tubes and the first tube form a substantially continuous passageway, such that aqueous humor flows from the anterior chamber into Schlemm""s canal through the substantially continuous passageway.
Another object of the present invention is to provide a seton, wherein the two wing tubes extend substantially perpendicular from the first tube.
Still another object of the present invention is to provide a seton, wherein the wing tubes have an outer diameter being no more than approximately 200 microns.
Yet another object of the present invention is to provide a seton, wherein the two wing tubes are tapered.
Further, another object of the present invention is to provide a seton, wherein the two wing tubes have an inner diameter ranging from substantially 80 microns to substantially 100 microns.
Still yet another object of the present invention is to provide a seton, wherein the first tube has an inner diameter ranging from substantially 280 microns to substantially 380 microns.
Another object of the present invention is to provide a seton, wherein the first tube has an outer diameter ranging from substantially 580 microns to substantially 680 microns.
Still another object of the present invention is to provide a seton, wherein the length of the first tube is approximately 1.5 cm.
Yet another object of the present invention is to provide a seton, wherein each of the two wing tubes has a length of approximately 1 cm.
Further, yet another object of the present invention is to provide a seton, wherein the first tube and the two wing tubes are composed of a biologically inert material.
Still another object of the present invention is to provide a seton, wherein the biologically inert material is silicone.
Still yet another object of the present invention is to provide a seton, further comprising at least one tab attached to one of the wing tubes, the tab having a fixation hole defined therein for securing the seton.
Yet another object of the present invention is to provide a seton, further comprising at least one port for clearing obstructions in the seton.
Further, another object of the present invention is to provide a seton, wherein the port may be defined in the first tube, in one of the two wing tubes, or in the intersection area formed by the first tube and the two wing tubes.
Another object of the present invention is to provide a seton, wherein the port is adapted for measuring intraocular eye pressure.
Still another object of the present invention is to provide a seton, further comprising pressure reading means for transmitting intraocular pressure readings to a pressure controller. In this embodiment the pressure controller is the pumping mechanism.
Yet another object of the present invention is to provide a method for draining aqueous humor from an associated anterior chamber of an eye, the method comprising the steps of providing an eye having a sclera and Schlemm""s canal; providing a seton having a first tube and two wing tubes, the first tube adapted to be inserted into an associated anterior chamber of the eye, the two wing tubes extending from the first tube, the two wing tubes adapted to be inserted into Schlemm""s canal, the two wing tubes and the first tube forming a substantially continuous passageway, whereby aqueous humor flows from the anterior chamber into Schlemm""s canal through the substantially continuous passageway; dissecting the sclera so as to form a scleral flap and an intrascleral space, with or without the removal of scleral tissue; cutting Schlemm""s canal to provide cut ends; inserting the first tube into the anterior chamber; inserting the two wing tubes into the cut ends of Schlemm""s canal; closing the scleral flap, or otherwise covering the seton; and, draining aqueous humor from the anterior chamber to the Schlemm""s canal.
Another object of the present invention is to provide a method for draining aqueous humor from an associated anterior chamber of an eye, further comprising the step of suturing the seton to the eye wall.
Still yet another object of the present invention is to provide a method for draining aqueous humor from an associated anterior chamber of an eye, further comprising the step of clearing obstructions disposed in the wing tubes through the port.
Further, another object of the present invention is to provide a method for draining aqueous humor from an associated anterior chamber of an eye, further comprising the step of monitoring aqueous outflow to assure proper placement of the wing tubes. It is to be understood that monitoring the flow has other purposes as well.
Still another object of the present invention is to provide a method for draining aqueous humor from an associated anterior chamber of an eye, further comprising the step of measuring intraocular pressure through the port.
According to another aspect of the present invention a device for directing aqueous humor from an anterior chamber to Schlemm""s canal comprises a seton and a pumping mechanism operatively connected to the seton.
Another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism is adapted to draw aqueous humor from the anterior chamber through the first tube, into the wing tubes, and into Schlemm""s canal.
Still another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the first tube extends into the pumping mechanism and the two wing tubes extend outwardly from the pumping mechanism.
Further, yet another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism is implanted within an intrascleral dissection. The pumping mechanism can also be located on the surface of the sclera.
Yet another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pump has dimensions of approximately 2 mm long by approximately 2 mm wide by approximately 500 microns in thickness.
Another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism is implanted between associated rectus muscles.
Still yet another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism is implanted posterior to an associated limbus.
Further, another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism has length, width, and thickness dimensions of approximately 6 mm by approximately 10 mm by approximately 3 mm, respectively.
Another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism is adapted to operate on a demand basis, such that the required flow through the two wing tubes, to achieve the desired intraocular pressure, varies according to the diurnal fluctuation in aqueous production.
Still yet another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, further comprising a feedback mechanism for monitoring work performed by the pumping mechanism to achieve the desired intraocular pressure.
Further yet, another object of the present invention is to provide a device for directing aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism is adapted to be adjusted without having to surgically dissect tissues to expose a large portion of the pumping mechanism.
According to another aspect of the present invention is to provide a method of draining aqueous humor from an anterior chamber to Schlemm""s canal, the method comprising the steps of providing an eye having a sclera and Schlemm""s canal; providing a seton and a pumping mechanism operatively connected to the seton, the seton having a first tube and two wing tubes, the first tube adapted to be inserted into an associated anterior chamber of the eye, the two wing tubes extending from the first tube, the two wing tubes adapted to be inserted into Schlemm""s canal, the two wing tubes and the first tube forming a substantially continuous passageway, whereby aqueous humor flows from the anterior chamber into Schlemm""s canal through the substantially continuous passageway; dissecting the sclera so as to form a scleral flap and an intrascleral space; cutting Schlemm""s canal to provide cut ends; inserting the first tube into the anterior chamber; inserting the two wing tubes into the cut ends of Schlemm""s canal; closing the scleral flap; activating the pump; and, draining aqueous humor from the anterior chamber to the Schlemm""s canal.
In accordance with yet another aspect of the present invention, a device for directing associated aqueous humor from an associated anterior chamber to an associated Schlemm""s canal includes a seton having a first tube adapted to be inserted into the anterior chamber and a second tube extending from the first tube, the second tube adapted to be inserted into the Schlemm""s canal, the tubes forming a substantially continuous passageway, wherein the aqueous humor flows from the anterior chamber into the Schlemm""s canal through the substantially continuous passageway, the second tube forming third and fourth tubes at an associated limbus, and a pump mechanism operatively connected to the seton.
Another aspect of the present invention is to provide a method of draining aqueous humor from an anterior chamber to Schlemm""s canal, further comprising the step of implanting the pumping mechanism within the intrascleral dissection, or other ocular surface.
Still another aspect of the present invention is to provide a method of draining aqueous humor from an anterior chamber to Schlemm""s canal, further comprising the step of implanting the pumping mechanism between rectus muscles.
Yet another aspect of the present invention is to provide a method of draining aqueous humor from an anterior chamber to Schlemm""s canal, wherein the pumping mechanism is implanted posterior to a limbus.
Further, another aspect of the present invention is to provide a method of draining aqueous humor from an anterior chamber to Schlemm""s canal, further comprising the steps of varying pumping mechanism output; and, achieving desired intraocular pressure according to diurnal fluctuation in aqueous humor production.
Another aspect of the present invention is to provide a method of draining aqueous humor from an anterior chamber to Schlemm""s canal, further comprising the step of decreasing pumping mechanism output when a predetermined intraocular pressure is reached.
According to another aspect of the invention, the process relies on the known pressure gradient between the anterior chamber and the venous circulation to permit the desired level of aqueous runoff and intraocular pressure.
Still yet, according to another aspect of the invention, the device contains a control port within the portion of the device that is positioned in the scleral dissection.